1. Field of the Invention
The present invention relates to an adjusting method of a battery pack and an adjusting method of a battery pack with a controller.
2. Description of Related Art
Recently, there have been proposed various secondary batteries as a power source of a portable device, a mobile device, and the like or a power source of an electric vehicle, a hybrid electric vehicle, and the like. In the case where this secondary battery is used as a power source of the electric vehicle, the hybrid electric vehicle, and the like, which demands high output power, a plurality of secondary batteries is electrically connected in series to constitute a battery pack.
Meanwhile, in the battery pack used as the power source of the electric vehicle, the hybrid electric vehicle, and the like, some of the secondary batteries constituting the battery pack may come to the end of their lives or be damaged earlier than other secondary batteries due to their use environment, differences in characteristics between secondary batteries of the battery pack, defects of components of each secondary battery. This may cause troubles that the battery pack could not bring out its inherent performance, leading to abnormal conditions of the entire system. To solve such troubles, there may be a case where the secondary battery that has come to the end of its life or has been broken earlier than other batteries is replaced with a normal one. This replacement method of secondary battery has been proposed variously (e.g. JP2004-185915A).
JP'915A discloses a method of replacing some secondary batteries of a battery pack, which includes a plurality of secondary batteries electrically connected in series or in parallel, with new ones by reducing a charge level of the new secondary battery than charge levels of other batteries not to be replaced (i.e. existing normal secondary batteries of the battery pack). JP'915A teaches the following concrete configuration. The new secondary battery for replacement is charged in advance so that the charge level of the new secondary battery is lower by 5% to 20% than the charge levels of the existing batteries not to be replaced. As charge and discharge is repeated during use of the battery pack, accordingly, a difference in the charge level (electric quantity) between the new secondary battery and other secondary batteries becomes smaller and consequently the charge levels of secondary batteries of the battery pack can be made equal to one another. JP'915A mentions that the performance of the battery pack can be enhanced to the maximum.
Meanwhile, for mounting on the electric vehicle, the hybrid electric vehicle, and the like, the battery pack is sometimes mounted in the form of a battery pack with a battery controller for detecting battery voltage (electromotive force) and temperature of each secondary battery of the battery pack, estimating a charge level (a charged electric quantity) based on those detected values, and monitoring whether the presence of a secondary battery whose charge level is abnormal. When a battery pack in which secondary batteries are replaced according to the method of JP'915A is used for this battery pack with controller (controller-equipped battery pack), the battery controller might detect an abnormal charge level of the secondary battery.
For instance, in the case where a charge level of a new secondary battery is too lower than that of other batteries at the time of battery replacement, abnormality in charge level may be detected just after the controller-equipped battery pack is mounted on a hybrid electric vehicle or the like. This is because the new secondary battery has been reduced in charge level by up to 20% as compared with other batteries and thus battery voltage may also have been reduced as compared with other batteries.
Further, the new secondary battery is superior in charge-discharge characteristics to other existing batteries not replaced. If the battery pack is used for a long period with repeat of charge and discharge, the charge level of the new secondary battery may become larger than the charge levels of other secondary batteries. As a result, the battery controller judges that the charge level of the new secondary battery is too larger than the charge levels of other batteries and determines the charge level of the new secondary battery to be abnormal.
If the secondary batteries of the battery pack include some secondary batteries whose charge levels have become too larger than other batteries, for example, the corresponding secondary battery or batteries are discharged so that the charge level(s) thereof comes close to the charge levels of other secondary batteries. This is because the performance of the battery pack can be brought out. However, such adjustment of charge level could solve the charge level problem but cause the following disadvantages. Specifically, the level of battery voltage of the discharged secondary battery would be excessively decreased as compared with the battery voltage of other secondary batteries (a battery voltage difference would exceed a normal range). Thus, the battery controller may judge the battery voltage as abnormal and determine that the charge level estimated based on the battery voltage is abnormal.